Dye loaded zeolite material

ABSTRACT

The present invention provides a dye loaded zeolite material comprising: a) at least one zeolite crystal having straight through uniform channels each having a channel axis parallel to, and a channel width transverse to, a c-axis of crystal unit cells; b) closure molecules having an elongated shape and consisting of a head moiety and a tail moiety, the tail moiety having a longitudinal extension of more than a dimension of the crystal unit cells along the c-axis and the head moiety having a lateral extension that is larger than said channel width and will prevent said head moiety from penetrating into a channel; c) a channel being terminated, in generally plug-like manner, at least at one end thereof located at a surface of the zeolite crystal by a closure molecule hose tail moiety penetrates into said chanel and whose head moiety substantially occludes said channel end while projecting over said surface; and d) an essentially linear arrangement of luminescent dye molecules enclosed within a terminated channel adjacent to at least one closure molecule and exhibiting properties related to supramolecular organization.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to the technical field of opticalmaterials and devices. In particular, the invention relates to a dyeloaded zeolite material; the invention further relates to a pigmentmaterial, a luminescent optical device, an optical sensor device, alight emitting device and a photonic energy harvesting device, all theaforesaid said comprising a dye loaded zeolite material.

[0003] 2. Description of the Prior Art

[0004] The structural, morphological, physical, and chemical variety ofzeolites has led to applications in different fields like catalysis, ionexchange, membranes, and chemical sensors where dynamic processesinvolving ions or adsorbate molecules play an important role (Thomas, J.M. Spektrum der Wissenschaft, June 1992, 88). Situations where thezeolites mainly serve as host for supramolecular organization ofmolecules, ions, complexes and clusters to prepare materials with newproperties such as non-linear optical (Cox, S. D.; Gier, T. E.; Stucky,G. D. Chem. Mater. 1990, 2, 609), quantum-size (Stucky, G. D.;MacDougall, J. E. Science 1990, 247, 669; Brühwiler, D.; Seifert, R.;Calzaferri, G. J. Phys. Chem B 1999, 103, 6397), micro laser (Vietze,U.; Krauss, O.; Laeri, F.; Ihnlein, G.; Schüth, F.; Limburg, B.;Abraham, M. Phys. Rev. Lett. 1998, 81, 4628) and artificial antennacharacteristics are new fields of growing interest (Wöhrle, D.;Schulz-Ekloff, G. Adv. Mater. 1994, 6, 875; Schüth, F. Chemie in unsererZeit 1995, 29, 45; Ozin, G. A.; Kuperman, A.; Stein, A. Angew. Chem1989, 101, 373.).

[0005] Some of these new materials can be considered as static andstable arrangements of guests in the zeolite host under a broad range ofconditions (Lainé, P.; Lanz, M.; Calzaferri, G. Inorg. Chem. 1996, 35,3514). In other cases, however, the adsorption, desorption or ionexchange of molecules or ions are reversible processes which lead to awide range of phenomena (Seifert, R.; Kunzmann, A.; Calzaferri, G.Angew. Chem. Inst. Ed. 1998, 37, 1521; Brühwiler, D.; Gfeller, N.;Calzaferri, G. J. Phys. Chem, B 1998, 102 ,2923; Ramamurthy, V.;Sanderson, D. R.; Eaton, D. F. J. Am. Chem. Soc. 1993, 115, 10438.).

[0006] Plants are masters of efficiently transforming sunlight intoenergy. In this process, every plant leaf acts as a photonic antennasystem, wherein photonic energy in the form of sunlight is transportedby chlorophyll molecules for the purpose of energy transformation.Accordingly, the synthesis, characterization and possible application ofan artificial photonic antenna for harvesting light within a certainvolume and for transport of the resultant electronic excitation energyto a specific location of molecular size has been the target of researchof several laboratories. Imaginative attempts to build an artificialphotonic antenna have been reported, including multinuclear luminescentmetal complexes, multichromophore cyclodextrines, Langmuir-Blodgettfilms, and dyes in polymers. Sensitization processes in silver halidephotographic materials as well as the spectral sensitization ofsemiconductor oxides also bear in some cases aspects of artificialphotonic antenna systems (“Energy Migration in Dye-Loaded HexagonalMicroporous Crystals”, Gfeller, N.; Calzaferri, G,. J. Phys. Chem. B1997, 101, 1396-1408 and references cited therein).

[0007] However, to our knowledge, the system reported by us in “FastEnergy Migration in Pyronine-Loaded Zeolite L Microcrystals”, Gfeller,N.; Megelski, S.; Calzaferri, G. J. Phys. Chem B 1999, 103, 1250-1257,is the first artificial photonic antenna that works well enough todeserve this name. In this artificial system, zeolite cylinders areadopted for forming a bidirectional photonic antenna wherein the lighttransport is made possible by specifically organized dye molecules thatmimic the natural function of chlorophyll. Zeolites are materials withdifferent cavity structures. Some of them occur in nature as a componentof the soil. We use zeolite L crystals of cylindrical morphology whichconsist of a continuous channel system and we have succeeded in fillingeach individual channel with chains of joined but noninteracting dyemolecules. Light shining on the cylinder is first absorbed and theenergy is transported by the dye molecules inside the channels to thecylinder ends (J. Phys. Chem. B 1997, 101, 1396-1408; “Transfer ofElectronic Excitation Energy between Dye Molecules in the Channels ofZeolite L”, Gfeller, N.; Megelski, S.; Calzaferri, G. J. Phys. Chem B1998, 102, 2433-2436; “Zeolite Microcrystals as Hosts for SupramolecularOrganization of 30 Dye Molecules”, Calzaferri, G. Chimia 1998, 52,525-532; “Fast Energy Migration in Pyronine-Loaded Zeolite LMicrocrystals”, Gfeller, N.; Megelski, S.; Calzaferri, G. J. Phys. ChemB 1999, 103, 1250-1257; “Dye Molecules in zeolite L nano crystals forefficient light harvesting”, Calzaferri, G. in Photofunctional Zeolites,Nova Science Publishers NY, Editor. M. Anpo, 2000, 205-218; Pauchard,M.; Deveaux, A.; Calzaferri, G. “Dye-Loaded Zeolite L Sandwiches”,CHEMISTRY a Eur. J. 2000, 6, 3456-3470).

[0008] We have previously synthesized nanocrystalline zeolite Lcylinders ranging in length from 300 nm to about 3000 nm. A cylinder of600 nm consists of, for example, about 100'000 channels arrangedessentially parallel to each other. A typical zeolite L material of thiskind is shown in FIG. 1. Single molecules of the luminescent dyeoxonine, which is capable of emitting light in the red wavelength range,were inserted into ends of the zeolite's channels that had previouslybeen filled with the luminescent dye pyronine, which is capable ofemitting light in the green wavelength range. By means of thisarrangement, experimental proof was furnished that efficient lighttransport is possible in such zeolite systems. Light of appropriatewavelength impinging on the zeolite is absorbed by pyronine moleculesonly. After such an absorption process, the energy moves along themolecules in the zeolite channel until it reaches a terminal oxoninemolecule. The oxonine absorbs the energy by a radiationless energytransfer process, but is not able to send the energy back to thepyronine. Instead, it emits the energy in the form of red light, visibleto the naked eye.

[0009] We have developed two methods for preparing suitable dye loadedzeolite materials, one method working at a solid/liquid interface andthe other method working at a solid/gas interface. Other approaches forpreparing similar materials are in situ and crystallization inclusionsynthesis. In our previous work, cationic dyes have been inserted intothe channels of zeolite L via ion exchange from a suspension, thusleading to zeolite L materials with donor molecules located in themiddle and acceptor molecules at the channel ends. After selectiveelectronic excitation of the donor molecules, fast energy migrationalong the c-axis and energy transfer at the channel ends to the acceptormolecules was observed. Subsequently, we have succeeded in preparingthree-dye-loaded zeolite L sandwiches. The general concept of thepreparation method of these materials is illustrated in FIG. 2 and aselection of molecules that have been studied is given in FIG. 3. First,a neutral dye molecule is inserted e.g. from the gas phase, filling thechannels to the desired degree. Provided that the inserted molecules arenot rapidly displaced by water, this material can then be ion exchangedwith a second dye. This can be well controlled, so that a specificallydesired space is left for the third dye, which is either inserted in anext ion exchange process, or from the gas phase. We have shown that bythese means a bidirectional antenna for light collection and transportcan been prepared so that the whole light spectrum can be used,transporting light energy from blue to green to red.

[0010] Within the context of this work several reactions and equilibriaplay a role and have been discussed: Insertion reaction of neutral dyes,adsorption at the outer surface, hydration, displacement and reinsertionreactions, and cation exchange. Many data have been obtained forp-terphenyl (pTP). The size of pTP and its chemical properties make itan excellent model for studying relevant parameters and for developingnew preparation methods. The first bi-directional three-lye-zeolite Lsandwich antenna has been realized with DPH as first luminescent dye. Wehave observed that the energy of near UV light that is absorbed in themiddle part of the antenna by DPH is transferred to adjacent pyroninemolecules, i.e. to the second luminescent dye, along which it migratesuntil it reaches the pyronine/oxonine interface, where a further energytransfer occurs from pyronine to oxonine, i.e. to the third luminescentdye (Calzaferri, G.; BrüIhwiler, D.; Megelski, S.; Pfenniger, M.;Pauchard, M.; Hennessy, B.; Maas, H.; Déveaux, A.; Graf, U. “Playingwith Dye Molecules at the Inner and Outer Surface of Zeolite L”, SolidState Sciences, 2000, Volume 2, 421-447, incorporated herein byreference).

[0011] Beyond being usable for a light harvesting system, the principlesdescribed are expected to be exploitable in numerous other applications.However, the dye loaded zeolite materials and any devices made thereofthat have so far been described, exhibit a number of significantshortcomings and disadvantages. In particular, the stability of suchsystems is still unsatisfactory, mainly because of an undesirablemigration of the luminescent dye molecules out of the zeolite channelsresulting in a depletion of the dye loaded zeolite material.

[0012] Moreover, the tasks of external trapping of excitation energyor - conversely of injecting energy at a specific point of the photonicantenna, the realization of a mono-directional photonic antenna and thecoupling of such photonic antennae to specific devices have not beensolved so far.

SUMMARY OF THE INVENTION

[0013] Accordingly, it is an object of the present invention to overcomethe above discussed shortcomings and disadvantages associated with thedye loaded zeolite materials and any devices made thereof that have sofar been described.

[0014] In particular, it is an object of this invention to provide a dyeloaded zeolite material that is suitable for a wide variety ofapplications and that shows improved stability as compared to known dyeloaded zeolite materials.

[0015] Further objects of this invention are to provide a pigmentmaterial showing improved stability, to provide a luminescent opticaldevice, to provide an optical sensor device, to provide a light emittingdevice and to provide a photonic energy harvesting device.

[0016] According to one aspect of this invention, there is provided adye loaded zeolite material comprising:

[0017] a) at least one zeolite crystal having straight through uniformchannels each having a channel axis parallel to, and a channel widthtransverse to, a c-axis is of crystal unit cells;

[0018] b) closure molecules having an elongated shape and consisting ofa head moiety and a tail moiety, the tail moiety having a longitudinalextension of more than a dimension of the crystal unit cells along thec-axis and the head moiety having a lateral extension that is largerthan said channel width and will prevent said head moiety frompenetrating into a channel;

[0019] c) a channel being terminated, in generally plug-like manner, atleast at one end thereof located at a surface of the zeolite crystal bya closure molecule whose tail moiety penetrates into said channel andwhose head moiety substantially occludes said channel end whileprojecting over said surface; and

[0020] d) said zeolite material further comprising an essentially lineararrangement of luminescent dye molecules enclosed within a terminatedchannel adjacent to at least one closure molecule and exhibitingproperties related to supramolecular organization.

[0021] According to a further aspect of this invention, there isprovided a pigment material showing improved stability, comprising a dyeloaded zeolite material as set forth hereinabove.

[0022] According to another aspect of this invention, there is provideda luminescent optical device comprising a dye loaded zeolite material asset forth hereinabove, wherein said dye molecules are selected such asto have a substantial luminescence quantum yield for a predeterminedexcitation wavelength.

[0023] According to a still further aspect of this invention, there isprovided an optical device comprising a dye loaded zeolite material asset forth hereinabove, wherein said dye molecules are selected such asto have a substantial luminescence quantum yield for a predeterminedexcitation wavelength, and wherein said closure molecule and said dyemolecules are capable of interacting in such manner that an externalinfluence exerted on the head moiety of the closure molecule results ina change of said luminescence quantum yield.

[0024] According to another aspect of this invention, there is provideda segmented dye loaded zeolite material comprising:

[0025] a) at least one zeolite crystal having straight through uniformchannels each having a channel axis parallel to, and a channel widthtransverse to, a c-axis of crystal unit cells;

[0026] b) closure molecules having an elongated shape and consisting ofa head moiety and a tail moiety, the tail moiety having a longitudinalextension of more than a dimension of the crystal unit cells along thec-axis and the head moiety having a lateral extension that is largerthan said channel width and will prevent said head moiety frompenetrating into a channel;

[0027] c) a channel being terminated, in generally plug-like manner, atleast at one end thereof located at a surface of the zeolite crystal bya closure molecule whose tail moiety penetrates into said channel andwhose head moiety substantially occludes said channel end whileprojecting over said surface; and

[0028] d) an essentially linear arrangement of luminescent dye moleculesenclosed within a terminated channel and exhibiting properties relatedto supramolecular organization, said arrangement comprising at least twosegments disposed in a sequence of adjacent segments, each segmentcomprising an essentially linear arrangement of identical dye molecules,at least one of said segments forming a terminal segment adjacent at oneend thereof to a closure molecule, the dye molecules in each one of saidsegments having an optical transition system comprising an absorptionband and an emission band, said absorption band being generallyblue-shifted and said emission band being generally red-shifted from anominal wavelength of the optical transition system, the dye moleculesof adjacent segments having respective optical transition systems insubstantial spectral overlap with each other, said sequence of adjacentsegments being spectrally ordered with respect to said nominalwavelengths.

[0029] According to yet another aspect of this invention, there isprovided a light emitting device comprising a segmented dye loadedzeolite material, as set forth hereinabove, wherein said sequence ofadjacent segments is spectrally ordered with said nominal wavelengthsincreasing along said sequence away from said terminal segment, saidclosure molecule and the dye molecules of said terminal segment beingcapable of interacting in such manner that energization of the headmoiety of the closure molecule results in an energy transfer to theoptical transition system of the dye molecules of said terminal segment.

[0030] According to still another aspect of this invention, there isprovided a photonic energy harvesting device comprising a segmented dyeloaded zeolite material as set forth hereinabove, wherein said sequenceof adjacent segments is spectrally ordered with said nominal wavelengthsdecreasing along said sequence away from said terminal segment, saidclosure molecule and the dye molecules of said terminal segment beingcapable of interacting in such manner that energization of the opticaltransition system of the dye molecules of said terminal segment resultsin an energy transfer to the head moiety of the closure molecule.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above mentioned and other features and objects of thisinvention and the manner of achieving them will become more apparent andthis invention itself will be better understood by reference to thefollowing description of various embodiments of this invention taken inconjunction with the accompanying drawings, wherein:

[0032]FIG. 1 is a micrograph showing a Zeolite L material;

[0033]FIG. 2 is a scheme illustrating the preparation of a three-dyeloaded Zeolite L;

[0034]FIG. 3 shows examples of luminescent dye molecules that can beinserted in Zeolite L;

[0035]FIG. 4 shows relevant structures of Zeolite L and luminescent dyemolecules, namely: left side: a top view of Zeolite L, perpendicular tothe c-axis, displayed as stick-representation (upper panel) and as Vander Waals representation with an oxonine molecule entering the zeolitechannel (lower panel), and eight side: a side view of a channel alongthe c-axis, without bridging oxygen atoms (upper panel), and thestructures of oxonine cation Ox⁺(top), pyronine cation Py⁺(middle) andPOPOP (bottom) with atom to atom distances and the coordinate system(lower panel);

[0036]FIG. 5 shows structure of typical closure molecules acting as aninjector-, acceptor-, or simply as a stopcock; the positive charge beingdesirable for anionic zeolite hosts and the zero charge being applicablefor all cases;

[0037]FIG. 6 shows examples of closure molecules with head moieties thatcan act as acceptor-heads but also as donor-heads, depending on the typeof dye molecules residing inside of the channels;

[0038]FIG. 7 shows further examples of luminescent dye molecules;

[0039]FIG. 8 shows examples of segmented dye loaded zeolite systems;

[0040]FIG. 9 shows the principle of an inverted antenna system; and

[0041]FIG. 10 shows a functionalized bidirectional inverted antennawhich forms the basis of a light emitting device.

[0042] The exemplifications set out herein are not to be construed aslimiting the scope of this disclosure or the scope of this invention inany manner.

DETAILED DESCRIPTION OF THE INVENTION

[0043] 1. Zeolite Materials

[0044] Zeolite materials suitable to act as hosts for supramolecularorganization of molecules, particularly luminescent dye molecules, havebeen described (see references cited in the description of the priorart) The present work is based on the known materials Zeolite L andZeolite ZSM-12. While these nanoporous materials have favorableproperties, they are not, however, the only ones that could be used toproduce the materials and devices described hereinbelow. Nevertheless,we will henceforth concentrate on Zeolite L nano crystals as shown inFIG. 1, noting that an even more homogeneous size distribution as theone shown can be obtained by applying size selective sedimentation.

[0045] Said Zeolite L nano crystals exhibiting cylinder morphology havestraight through uniform channels each having a channel axis parallelto, and a channel width transverse to, a c-axis of crystal unit cells.As an essential feature of the present invention, closure molecules areprovided having an elongated shape and consisting of a head moiety and atail moiety, the tail moiety having a longitudinal extension of morethan a dimension of the crystal unit cells along the c-axis and the headmoiety having a lateral extension that is larger than said channel widthand will prevent said head moiety from penetrating into a channel.Accordingly, said channel is terminated, in generally plug-like manner,at least at one end thereof located at a surface of the zeolite crystalby a closure molecule whose tail moiety penetrates into said channel andwhose head moiety substantially occludes said channel end whileprojecting over said surface. Within such terminated channel,luminescent dye molecules are enclosed, forming an essentially lineararrangement and exhibiting properties related to supramolecularorganization.

[0046] 2. Closure Molecules

[0047] A common principle of closure molecules is that they consist of ahead moiety and a tail moiety, the head moiety being too large to enterinto a channel of the zeolite host, whereas the tail moiety canpentetrate into the end of said channel. Similar to a cork on asparkling-wine bottle, the head moiety substantially occludes in aplug-like manner the channel end while projecting over a surface of thezeolite crystal.

[0048] There are many different embodiments of such closure molecules,which should be chosen depending on the specific type of applicationenvisioned and depending on the type of zeolite host material used.

[0049] One may distinguish between hosts with an anionic framework suchas Zeolite L or ZSM-12 and hosts with a neutral framework, such asAlPO₄-5 or VPI-5. No substantial difference in respect of these twotypes of host materials arises in those cases where the tail moiety isessentially electroneutral. In contrast, closure molecules with apositively charged tail moiety appear to be particularly interesting inconjunction with anionic hosts such as Zeolite L.

[0050] In order to understand the prinicples and constraints regardingthe interaction between closure molecules and zeolite host, one shouldconsider the relevant structural parameters as shown in FIG. 4. Thegeometrical constraints imposed by the host determine the organizationof the luminescent dye molecules within the channels and further definewhat types of closure molecules are able to fulfill the desiredfunction. The main channels of Zeolite L consist of unit cells with alength of 7.5 Å in the c-direction, as illustrated in FIG. 4. The unitcells are joined by shared 12-membered ring windows having a freediameter of 7.1-7.8 Å. The largest free diameter is about 13 Å,depending on the charge compensating cations. It lies midway between the12-membered rings. The lengths of the primitive vectors a and b are 18.4Å. For example, a zeolite L crystal of 500 nm diameter and 375 nm lengthgives rise to about 67'000 parallel channels, each of which consists of500 unit cells.

[0051] The three molecules displayed on the right hand side of FIG. 4illustrate the typical size of molecules that can penetrate into thechannels of zeolite L. However, these molecules are typical only fromthe point of view of their size, not from the point of view of theirproperties, because they do absorb light in the visible or in the nearUV. In contrast, suitable tail moieties typically do not absorb light ofa wavelength longer than about 300 nm.

[0052] The general structural characteristics illustrated in FIG. 5 aredesirable for a closure molecule. The diameter h of the head moietiesshould be larger than about 8 Å and the length t of the tail should besuch that it penetrates at least one unit cell (this means 6 Å or morefor zeolite L).

[0053] 3. Tail Moieties

[0054] Tail moieteis are generally based on organic or silicon/organicframeworks. Typical tail moieties will not absorb light of a wavelengthlonger than about 300 nm. However, exceptions do exist. Three types oftail moieties play a role, depending on the desired properties: (i) nonreactive tail moieties; (ii) tail moieties that can undergo anisomerization process after insertion in a channel end under theinfluence of irradiation, heat or a reactive species that issufficiently small; (iii) reactive tail moieties that can bind tomolecules inside of the channels. It appears sufficient to provide someexamples of closure molecules with type (i) tail moieties, because forcases (ii) and (iii) a wide spectrum of suitable reactions is known.

[0055] 4. Head Moieties

[0056] Independently of its specific application, any head moiety mustbe large enough so that it cannot enter into a channel of the zeolitematerial. As a consequence of this general condition, any suitable headmoiety will also substantially occlude the end of a channel into whichthe respective tail moiety is inserted, and it will project over thesurface of the zeolite crystal at which said channel ends. In addition,head moieties must fulfill any stability criteria imposed by a specificapplication. In general, head moieties will comprise an organic, asilicon-organic or a coordination-type entity.

[0057] Advantageously, head moieties are selected so as to achieve adesired functionalization of the dye loaded zeolite's surface propertiessuch as the wetting ability, the refractive index matching or thereactivity. For example, it might be desirable to select a closuremolecule with a head moiety bearing reactive “arms”, so that afterloading the zeolite material an additional process could occur, wherebyreactive arms of head moieties located near the ends of neighbouringchannels could interact with each other to form a monolayer type polymerat the surface of the zeolite crystal.

[0058] Particular types of head moieties include acceptor-heads anddonor-heads. Acceptor-heads serve to accept an excitation energytransferred to them by a nearby dye molecule located within the channel.In general, acceptor-heads are strongly luminescent entities having alarge spectral overlap with the dye molecules located inside of thechannels. In contrast, donor-heads must be able to transfer an initiallyreceived excitation energy to a nearby dye molecule located within thechannel. These energy transfer processes are generally radiationless,mostly based on dipole-dipole coupling.

[0059] Since luminescence is quenched by dimerization, the head moietiesshould be prevented from interacting electronically with each other. Forthis purpose, it may be necessary to shield a chromophoric part of ahead moiety by attaching to it one or more inactive substituents such asaliphatic groups.

[0060] While a large number of chemical entities could be used as headmoieties, practical constraints of various type might limit theselection based on requirements for stability, particular shape,non-toxicity and so forth.

[0061] 5. Examples of Closure Molecules

[0062] A small selection of commercially available molecules suitable asclosure molecules is compiled in FIG. 6, showing, from the top to thebottom:

[0063]6-(((4-(4,4-difluoro-5-(2-thienyl)-4-bora-3a,4a-diaza-s-indacene-3-yl)phenoxy)acetyl)amino)hexanoicacid succinimidyl ester,

[0064] a schematic representation of a closure molecule;

[0065]4,5-difluoro-5,7-diphenyl-4-bora-3a,4a-diaza-s-indacene-3-propionylethylenediamine hydrochloride;

[0066] “Molecule C”; and

[0067] “Molecule D”.

[0068] A further compound usable as closure molecule is4-(4-(dilinolethylamino)stiryl)N-methylpryidinium. Still further closuremolecules can be constructed, that comprise a head moiety such as asubstituted porphyrin, a substituted rhodamine, a substitutedruthenium-tris-bipyridine or a substituted C₆₀.

[0069] 6. Luminescent Dyes

[0070] There is a very large number of luminescent dye molecules thatare generally suited for insertion into the channels of Zeolite L, manyof which have been specifically described in the literature citedhereinabove. We will simply mention the molecules shown in FIG. 3, i.e.biphenyl, pyronine, p-terphenyl, oxonine, 1,6-diphenylhexatriene,resorufin, 1,2-bis-(5-methyl-benzoxazol-2yl)-ethene and4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, the latter being alsoknown as Hydroxy-TEMPO. Further suitable luminescent dye molecules arep-bis[2-(5-phenyloxazolyl)]benzene, also known as POPOP, as well as thedye molecules listed in Table 2 of “Zeolite Microcrystals as Hosts forSupramolecular Organization of Dye Molecules”, Calzaferri, G. Chimia1998, 52, 525-532, which is explicitly incorporated herein by reference.Still further suitable luminescent dye molecules are shown in FIG. 7,which shows, from top to the bottom:

[0071] pyronine G,

[0072] fluorenone,

[0073] trans-4-dimethly-amino-4′cyanostilbene,

[0074] trans-4-acetidinyl-4′-cyanostilbene, and

[0075] 1,4-bis(4-methyl-5-phenyl-2-oxazolyl)-benzene (also known asdimethyl-POPOP).

[0076] 7. Dye Loaded Zeolite Materials

[0077] In the simplest case, a dye loaded zeolite material as describedhereinabove comprises an essentially linear arrangement of luminescentdye molecules enclosed within a terminated channel. This arrangement isadjacent to at least one closure molecule. By virtue of their specificarrangement resembling a bead chain, a plurality of dye moleculesenclosed within a channel exhibits properties related to supramolecularorganization.

[0078] By extension of the principle just described, a segmented dyeloaded zeolite material can be envisioned as shown in FIG. 8, wherein anessentially linear arrangement of luminescent dye molecules enclosedwithin a terminated channel and exhibiting properties related tosupramolecular organization comprises at least two segments disposed ina sequence of adjacent segments. Each segment comprises an essentiallylinear arrangement of identical dye molecules. At least one of saidsegments forms a terminal segment that is adjacent at one end thereof toa closure molecule. The dye molecules in each one of said segments havean optical transition system comprising an absorption band and anemission band, said absorption band being generally blue-shifted andsaid emission band being generally red-shifted from a nominal wavelengthλ of the optical transition system. It should be noted that the terms“blue-shifted” and “red-shifted” are to be understood in the sense of“shifted to shorter wavelengths” and “shifted to longer wavelengths”,respectively, as customary in spectroscopy. The dye molecules ofadjacent segments have respective optical transition systems insubstantial spectral overlap with each other, and said sequence ofadjacent segments is spectrally ordered with respect to said nominalwavelengths.

[0079] Referring again to FIG. 8, a nano crystal of cylinder morphologywith a typical length of 600 nm is divided along its longitudinalchannel axis in 3 parts, e.g. with a length of ˜200 nm each. Thearrangement labelled as “System 1” in FIG. 8 simply shows the principleof a segmented arrangement comprising a first segment with dye moleculeshaving a nominal wavelength λ₁, a second segment with dye moleculeshaving a nominal wavelength λ₂ and a third segment with a dye having anominal wavelength λ₃, but without showing the respective closuremolecules at the channel end. The dye molecules are preferably stronglyluminescent and their nominal wavelengths fulfill the conditionλ₁<λ₂<λ₃. Moreover, the spectral overlap integral of the opticaltransition systems of the dye molecules in adjacent segments is large.In such an arrangement, very fast Förster-type energy migration alongthe z axis is expected, supported by self-absorption and re-emissionprocesses. The dimensions of the nano crystal are in the order of thewavelength of the light.

[0080] More specifically, “System 2” comprises a closure molecule Tplaced at the λ₃-end of the segmented arrangement. Closure molecule T,typically a porphyrine or a phthalocyanine, further acts as anacceptor-head enabled to function as an excitation trap. Conversely,“System 3” comprises a closure molecule I placed at the λ₁-end of thesegmented arrangement and acting as a donor-head capable to function asan energy injector. A segmented dye loaded zeolite crystal of the typedisplayed as “System 2” or “System 3” can be connected to a quantum sizeparticle, a semiconductor, a conductor, a conjugated polymer, a quartzfiber and so forth, depending on the application envisaged.

EXAMPLE 1 Applications of Zeolite Materials Loaded With One Dye

[0081] With the dye loaded zeolite materials described hereinabove, itis possible to produce luminescent dye pigments with extremely highbrilliance and stability. Materials with dye concentrationscorresponding to 0.4 mol/L wherein the dyes are present as monomers andtherefore are very luminescent and brilliant can easily be prepared,covering the whole visible spectrum. Independently of the dye used,these materials are nontoxic since the dye is encapsulated and cannot bereleased to the environment. Particle sizes between about 50 nm to 3000nm can be made, absorptivity and color can easily be tuned, andrefractive index coating is possible. Since the same basic zeolitematerial can be used for a large variety of dyes depending on theparticular application, a large simplification and hence an enormoustechnological advantage is achieved.

[0082] As a further application, scintillation materials with extremelyhigh sensitivity and versatility can be prepared with the dye loadedzeolite materials described hereinabove. It is simple to prepare stablelayers on e.g. a plastic material of any shape. Very thin layers (e.g.of a few hundred nm) with nearly 100% absorptivity can thus be prepared.

[0083] Moreover, the dye loaded zeolite materials described hereinabovecan be employed to build novel luminescent optical devices, such as dyelasers with dimensions of a few hundred nanometer, needles for scanningnear field microscopes and other highly integrated optical devices. Suchdevice could also encompass a highly efficient photosensitizer deviceapplicable, e.g. to photodynamic therapy of malignant tissues. Since theabsorptivity of a 50 nm dye zeolite particle is about 20'000 larger thanthat of a single dye molecules, the treatment could be carried out withmuch lower light intensity, which in some cases could be an importantadvantage.

EXAMPLE 2

[0084] Analytical Probes

[0085] Fluorescent molecules are used in many analytical applications inchemistry, biology including cell biology, medicine and environmentalsciences. Many substances specifically designed for such applicationsare available on the market under the general technical term of“fluorescent molecular probes”. In this context, a corresponding termfor the dye loaded zeolite materials described herein would be that of“fluorescent nanoprobes”. In comparison with conventional molecularprobes, said zeolite material can enhance the sensitivity by a factor ofup to about 100'000. Apart from this enormous amplification, nanoprobesbased on the dye loaded zeolite materials according to the presentinvention do not blink, that is, the luminescence signal emitted by themis continuous in time, which has important advantages in someapplications. Such nanoprobes can be made with sizes in the range ofabout 50 nm to 3000 nm, depending on the applications.

[0086] The number of unit cells of Zeolite L is given by N_(uc)=0.35nm⁻³d_(Z) ²(nm)I_(Z)(nm) (d_(Z)=diameter of the zeolite, I_(Z)=length ofthe zeolite, both in nm). Hence, a 100 nm zeolite crystal consists of350'000 unit cells. A typical dye molecule occupies 2 to 3 unit cells.This means that a 100 nm particle contains about 100'000 chromophores(dye molecules). A 50 nm crystal contains correspondingly 43'750 unitcells, which means up to about 20'000 chromophores. Each of them canabsorb a light quantum coming in (this means that the probability ofe.g. a 100 nm dye loaded crystal to absorb a light quantum is 100'000larger than that of a single molecule).

[0087] A system for which efficient energy transfer has been foundcomprises a Zeolite L loaded with pyronine cations as dye molecules andprovided with6-(((4-(4,4-difluoro-5-(2-thienyl)-4-bora-3a,4a-diaza-s-indacene-3-yl)phenoxy)acetyl)amino)hexanoicacid succinimidyl ester (i.e. the top molecule in FIG. 6), also known asBODIPY® TR-X SE as closure molecules. Upon illumination with green lightcausing electronic excitation of the entrapped dye molecules, a rapidtransfer of energy to the head moieties of the closure molecules occurs,thus resulting in substantial fluorescence emission in the red spectralregion. It is found that the relative intensity of this red fluorescenceas compared to the intensity of the green fluorescence increases withincreasing concentration of entrapped pyronine dye.

[0088] Because of the extremely fast energy migration, we have observedthat in a dye loaded zeolite material according to the presentinvention, it is possible in favorable cases to quench this luminescencewith a probability of more than 95% by a single molecule undergoing aninteraction with a suitably chosen closure molecule. For example, aclosure molecule can be selected the behavior of which depends on thenature of complexing ions such as H⁺, alkali ions, Ca²⁺, and similar,but also closure molecules the behavior of which depends on localviscosity, local polarity, protein adsorption and other specificinteractions. Indeed, head moieties can be tailored in order to createhighly specific nanoprobes. Such nanoprobes could be used in combinationwith all common techniques, stationary and time resolved, such asconventional fluorescence measurements, standard and unconventionalmicroscopy techniques, fiber optic devices, etc. Optical sensing couldbe applied by monitoring a change of refractive index of an analytesolution in contact with the nanoprobe.

[0089] An efficient energy transfer has also been achieved in theopposite direction, i.e. from the closure molecule to the dye moleculesentrapped in the zeolite system. For this purpose, a Zeolite L loadedwith oxonine cations as dye molecules was provided with closuremolecules consisting of BODIPY® 493/503 SE. Upon illumination with greenlight causing electronic excitation of the stopcock molecules, a rapidtransfer of energy to the entrapped oxonine molecules occured, thusresulting in substantial fluorescence emission in the red spectralregion.

EXAMPLE 3 Light Emitting Devices

[0090] A segmented dye loaded zeolite material according to the presentinvention can be used to construct a light emitting device, for whichone needs to implement an inverted antenna system. An advantageousfeature of said zeolite materials is that light of any color of thewhole visible spectrum can be generated with basically the samematerial. Spatial resolution can be as low as 100 nm, since the limitsthereto are imposed by the properties of light, i.e. diffraction, not bythe material. We have recently been able to synthesize an invertedantenna system which can be explained by means of FIG. 9. Excitationtravels in a radiationless process from both ends of the crystal towardsthe middle where it is emitted. The amount of blue, green and redemission can be tuned by varying the characteristics, e.g. the length,of the different regions. This means that excitation covering the wholevisible spectrum can be generated by means of basically the samematerial.

[0091] Energy supply to the light emitting device occurs as shown in thearrangement of FIG. 10. Initially, a closure molecule provided with adonor-head acting as an injector I is excited, which readily transfersits excitation energy in a radiationless process to the blue dyemolecules in the adjacent terminal segment of the zeolite channel. Fromthere, the inverted antenna transports the excitation energysegment-wise towards the middle of the crystal, where it is finallyreleased as luminescence light. It is sufficient to connect with anexcitation source only one end of the two closure molecules located atopposite ends of a given channel.

[0092] It is important to note that with the same injector I and thesame blue dye in the terminal segment, light emission of any color canbe realized by just varying the characteristics of the green and the redparts of the inverted antenna.

EXAMPLE 4 Photonic Energy Harvesting Devices

[0093] As a further application of segmented dye loaded zeolite systemsaccording to the present invention, a new type of photonic energyharvesting device such as a solar cell can be realized. Such a devicecomprises a sequence of dye segments that is ordered in opposite orderas compared to the light emitting device mentioned hereinabove, and witha closure molecule featuring an acceptor-head. Light absorbed by the dyemolecules in one of the inner segments is efficiently transferred to theterminal segment and then to the closure molecule, from where it couldthen be fed into a suitable energy receiver or consumer system. Theadvantage of such a “dye sensitized solid state solar cell” with respectto current technologies is that in principle very cheap cells with veryhigh efficiency (more than 30% for tandem devices) can be made based onnontoxic materials.

[0094] While only the preferred and some typical embodiments of thisinvention have been described hereinabove, it will be understood thatthe invention is not limited to the embodiments disclosed, but isequally capable of numerous other equivalent arrangements,rearrangements, modifications and substitutions of parts and elements,equivalently to achieve the functions, means, ways and results disclosedherein, without departing from the spirit and teaching of the invention,and are embodied in this invention.

EXAMPLE 5 Loading of a Cationic Dye Into a Zeolite Preloaded With aNeutral Dye

[0095] Loading of a cationic dye like pyronine or pyronine G into azeolite already loaded with a neutral dye presents the followingdifficulty. While the cationic dye would usually be added from anaqueous solution, it turns out that water tends to displace any neutraldye molecules present in the zeolite, i.e. the neutral dye moleculeswould be removed from the zeolite when attempting to add the cationicdye molecules. Accordingly, it is preferable to use a solvent like1-butanol, which does not displace the neutral dye molecules from thezeolite. However, it turns out that the ion exchange reaction by meansof which a cationic dye molecule entering the zeolite replaces apotassium ion is prevented by the poor solubility of potassium ions in1-butanol. This problem is overcome by adding to the solution aso-called cryptand, a molecule with a very high affinity for potassiumions.

[0096] For example, samples of Zeolite L loaded with pyronine can beprepared by stirring a solution of pyronine in 1-butanol containing a13-fold excess of the known cryptand molecule Kryptofix222® and ZeoliteL at 50° C. for 44 hours.

1. A dye loaded zeolite material comprising: a) at least one zeolitecrystal having straight through uniform channels each having a channelaxis parallel to, and a channel width transverse to, a c-axis of crystalunit cells; b) closure molecules having an elongated shape andconsisting of a head moiety and a tail moiety, the tail moiety having alongitudinal extension of more than a dimension of the crystal unitcells along the c-axis and the head moiety having a lateral extensionthat is larger than said channel width and will prevent said head moietyfrom penetrating into a channel; c) a channel being terminated, ingenerally plug-like manner, at least at one end thereof located at asurface of the zeolite crystal by a closure molecule whose tail moietypenetrates into said channel and whose head moiety substantiallyoccludes said channel end while projecting over said surface; and d) anessentially linear arrangement of luminescent dye molecules enclosedwithin a terminated channel adjacent to at least one closure moleculeand exhibiting properties related to supramolecular organization.
 2. Thedye loaded zeolite material as defined in claim 1, wherein theluminescent dye molecules are selected from the group consisting ofbiphenyl, pyronine, p-terphenyl, oxonine, 1,6-diphenylhexatriene,resorufin, 1,2-bis-(5-methyl-benzoxazol-2yl)-ethene,p-bis[2-(5-phenyloxazolyl)]benzene,4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, pyronine G, fluorenone,trans-4-dimethly-amino-4′cyanostilbene,trans-4-acetidinyl-4′-cyanostilbene, and dimethyl-POPOP and wherein theclosure molecules are selected from the group consisting of6-(((4-(4,4-difluoro-5-(2-thienyl)-4-bora-3a,4a-diaza-s-indacene-3-yl)phenoxy)acetyl)amino)hexanoicacid succinimidyl ester,4,5-difluoro-5,7-diphenyl-4-bora-3a,4a-diaza-s-indacene-3-propionylethylenediamine hydrochloride, Molecule C, Molecule D, and4(4-(dilinolethylamino)stiryl)-N-methylpryidinium.
 3. A pigment materialshowing improved stability, comprising a dye loaded zeolite materialcomprising: a) at least one zeolite crystal having straight throughuniform channels each having a channel axis parallel to, and a channelwidth transverse to, a c-axis of crystal unit cells; b) closuremolecules having an elongated shape and consisting of a head moiety anda tail moiety, the tail moiety having a longitudinal extension of morethan a dimension of the crystal unit cells along the c-axis and the headmoiety having a lateral extension that is larger than said channel widthand will prevent said head moiety from penetrating into a channel; c) achannel being terminated, in generally plug-like manner, at least at oneend thereof located at a surface of the zeolite crystal by a closuremolecule whose tail moiety penetrates into said channel and whose headmoiety substantially occludes said channel end while projecting oversaid surface; and d) an essentially linear arrangement of luminescentdye molecules enclosed within a terminated channel adjacent to at leastone closure molecule and exhibiting properties related to supramolecularorganization.
 4. The pigment material as defined in claim 3, wherein theluminescent dye molecules are selected from the group consisting ofbiphenyl, pyronine, p-terphenyl, oxonine, 1,6-diphenylhexatriene,resorufin, 1,2-bis-(5-methyl-benzoxazol-2yl)-ethene,p-bis[2-(5-phenyloxazolyl)]benzene,4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, pyronine G, fluorenone,trans-4-dimethly-amino-4′cyanostilbene,trans-4-acetidinyl-4′-cyanostilbene, and dimethyl-POPOP and wherein theclosure molecules are selected from the group consisting of6-(((4-(4,4-difluoro-5-(2-thienyl)-4-bora-3a,4a-diaza-s-indacene-3yl)phenoxy)acetyl)amino)hexanoicacid succinimidyl ester,4,5-difluoro-5,7-diphenyl-4-bora-3a,4a-diaza-indacene-3-propionylethylenediamine hydrochloride, Molecule C, Molecule D, and4-(4-(dilinolethylamino)stiryl)-N-methylpryidinium.
 5. A luminescentoptical device comprising a dye loaded zeolite material comprising: a)at least one zeolite crystal having straight through uniform channelseach having a channel axis parallel to, and a channel width transverseto, a c-axis of crystal unit cells; b) closure molecules having anelongated shape and consisting of a head moiety and a tail moiety, thetail moiety having a longitudinal extension of more than a dimension ofthe crystal unit cells along the c-axis and the head moiety having alateral extension that is larger than said channel width and willprevent said head moiety from penetrating into a channel; c) a channelbeing terminated, in generally plug-like manner, at least at one endthereof located at a surface of the zeolite crystal by a closuremolecule whose tail moiety penetrates into said channel and whose headmoiety substantially occludes said channel end while projecting oversaid surface; and d) an essentially linear arrangement of luminescentdye molecules enclosed within a terminated channel adjacent to at leastone closure molecule and exhibiting properties related to supramolecularorganization, said dye molecules being selected such as to have asubstantial luminescence quantum yield for a predetermined excitationwavelength.
 6. The luminescent optical device as defined in claim 5,adapted for use in a device selected from a scintillation detector, ascanning near field optical microscope and a photosensitizer.
 7. Anoptical sensor device comprising a dye loaded zeolite materialcomprising: a) at least one zeolite crystal having straight throughuniform channels each having a channel axis parallel to, and a channelwidth transverse to, a c-axis of crystal unit cells; b) closuremolecules having an elongated shape and consisting of a head moiety anda tail moiety, the tail moiety having a longitudinal extension of morethan a dimension of the crystal unit cells along the c-axis and the headmoiety having a lateral extension that is larger than said channel widthand will prevent said head moiety from penetrating into a channel; c) achannel being terminated, in generally plug-like manner, at least at oneend thereof located at a surface of the zeolite crystal by a closuremolecule whose tail moiety penetrates into said channel and whose headmoiety substantially occludes said channel end while projecting oversaid surface; and d) an essentially linear arrangement of luminescentdye molecules enclosed within a terminated channel adjacent to at leastone closure molecule and exhibiting properties related to supramolecularorganization, said dye molecules being selected to have a substantialluminescence quantum yield for a predetermined excitation wavelength; e)said closure molecule and said dye molecules being capable ofinteracting in such manner that an external influence exerted on thehead moiety of the closure molecule results in a change of saidluminescence quantum yield.
 8. The optical sensor device as defined inclaim 7, adapted for use in an analytical probe.
 9. A segmented dyeloaded zeolite material comprising: a) at least one zeolite crystalhaving straight through uniform channels each having a channel axisparallel to, and a channel width transverse to, a c-axis of crystal unitcells; b) closure molecules having an elongated shape and consisting ofa head moiety and a tail moiety, the tail moiety having a longitudinalextension of more than a dimension of the crystal unit cells along thec-axis and the head moiety having a lateral extension that is largerthan said channel width and will prevent said head moiety frompenetrating into a channel; c) a channel being terminated, in generallyplug-like manner, at least at one end thereof located at a surface ofthe zeolite crystal by a closure molecule whose tail moiety penetratesinto said channel and whose head moiety substantially occludes saidchannel end while projecting over said surface; and d) an essentiallylinear arrangement of luminescent dye molecules enclosed within aterminated channel and exhibiting properties related to supramolecularorganization, said arrangement comprising at least two segments disposedin a sequence of adjacent segments, each segment comprising anessentially linear arrangement of identical dye molecules, at least oneof said segments forming a terminal segment adjacent at one end thereofto a closure molecule, the dye molecules in each one of said segmentshaving an optical transition system comprising an absorption band and anemission band, said absorption band being generally blue-shifted andsaid emission band being generally red-shifted from a nominal wavelengthof the optical transition system, the dye molecules of adjacent segmentshaving respective optical transition systems in substantial spectraloverlap with each other, said sequence of adjacent segments beingspectrally ordered with respect to said nominal wavelengths.
 10. Thesegmented dye loaded zeolite material as defined in claim 9, whereinsaid terminal segment comprises dye molecules with an optical transitionsystem in substantial spectral overlap with an optical transition systemof the closure molecule adjacent to said terminal segment.
 11. Thesegmented dye loaded zeolite material as defined in claim 9, whereinsaid sequence of adjacent segments is spectrally ordered with saidnominal wavelengths increasing along said sequence away from saidterminal segment.
 12. The segmented dye loaded zeolite material asdefined in claim 9, wherein said sequence of adjacent segments isspectrally ordered with said nominal wavelengths decreasing along saidsequence away from said terminal segment.
 13. A light emitting devicecomprising a segmented dye loaded zeolite material comprising: a) atleast one zeolite crystal having straight through uniform channels eachhaving a channel axis parallel to, and a channel width transverse to, ac-axis of crystal unit cells; b) closure molecules having an elongatedshape and consisting of a head moiety and a tail moiety, the tail moietyhaving a longitudinal extension of more than a dimension of the crystalunit cells along the c-axis and the head moiety having a lateralextension that is larger than said channel width and will prevent saidhead moiety from penetrating into a channel; c) a channel beingterminated, in generally plug-like manner, at least at one end thereoflocated at a surface of the zeolite crystal by a closure molecule whosetail moiety penetrates into said channel and whose head moietysubstantially occludes said channel end while projecting over saidsurface; and d) an essentially linear arrangement of luminescent dyemolecules enclosed within a terminated channel and exhibiting propertiesrelated to supramolecular organization, said arrangement comprising atleast two segments disposed in a sequence of adjacent segments, eachsegment comprising an essentially linear arrangement of identical dyemolecules, at least one of said segments forming a terminal segmentadjacent at one end thereof to a closure molecule, the dye molecules ineach one of said segments having an optical transition system comprisingan absorption band and an emission band, said absorption band beinggenerally blue-shifted and said emission band being generallyred-shifted from a nominal wavelength of the optical transition system,the dye molecules of adjacent segments having respective opticaltransition systems in substantial spectral overlap with each other, saidsequence of adjacent segments being spectrally ordered with said nominalwavelengths increasing along said sequence away from said terminalsegment; e) said closure molecule and the dye molecules of said terminalsegment being capable of interacting in such manner that energization ofthe head moiety of the closure molecule results in an energy transfer tothe optical transition system of the dye molecules of said terminalsegment.
 14. The light emitting device as defined in claim 13, whereinsaid sequence of adjacent segments comprises an internal segmentseparated from said closure molecule by at least one further segment.15. The light emitting device as defined in claim 14, wherein saidinternal segment extends along a substantial part of the respectivechannel.
 16. A photonic energy harvesting device comprising a segmenteddye loaded zeolite material comprising: a) at least one zeolite crystalhaving straight through uniform channels each having a channel axisparallel to, and a channel width transverse to, a c-axis of crystal unitcells; b) closure molecules having an elongated shape and consisting ofa head moiety and a tail moiety, the tail moiety having a longitudinalextension of more than a dimension of the crystal unit cells along thec-axis and the head moiety having a lateral extension that is largerthan said channel width and will prevent said head moiety frompenetrating into a channel; c) a channel being terminated, in generallyplug-like manner, at least at one end thereof located at a surface ofthe zeolite crystal by a closure molecule whose tail moiety penetratesinto said channel and whose head moiety substantially occludes saidchannel end while projecting over said surface; and d) an essentiallylinear arrangement of luminescent dye molecules enclosed within aterminated channel and exhibiting properties related to supramolecularorganization, said arrangement comprising at least two segments disposedin a sequence of adjacent segments, each segment comprising anessentially linear arrangement of identical dye molecules, at least oneof said segments forming a terminal segment adjacent at one end thereofto a closure molecule, the dye molecules in each one of said segmentshaving an optical transition system comprising an absorption band and anemission band, said absorption band being generally blue-shifted andsaid emission band being generally red-shifted from a nominal wavelengthof the optical transition system, the dye molecules of adjacent segmentshaving respective optical transition systems in substantial spectraloverlap with each other, said sequence of adjacent segments beingspectrally ordered with said nominal wavelengths decreasing along saidsequence away from said terminal segment; e) said closure molecule andthe dye molecules of said terminal segment being capable of interactingin such manner that energization of the optical transition system of thedye molecules of said terminal segment results in an energy transfer tothe head moiety of the closure molecule.
 17. The photonic energyharvesting device as defined in claim 16, wherein said closure moleculeis capable of converting an energy received from said terminal segmentto electric energy.
 18. The photonic energy harvesting device as definedin claim 16, wherein said closure molecule is capable of converting anenergy received from said terminal segment to photonic energy.